Coated paperboard

Abstract

The present disclosure provides a coated paperboard comprising a paperboard substrate and a coating wherein: the coating comprises a pigment mixture and a binder in a dry weight ratio in the range of from 100: 14 to 100: 25; the pigment mixture includes a calcium carbonate pigment and a clay pigment in a dry weight ratio ranging from 98: 2 to 92: 8; and the calcium carbonate pigment has a particle size distribution (wt.% lt; 2 [mu] m) is in the range of 75 to 95.

Description

Technical Field

[0001] The present disclosure relates to the field of coated paperboards. Background Art

[0002] Paperboards are typically coated with one or more coatings before use. Some coatings can impart barrier properties against oxygen or water, while others can impart surface properties such as improved printability and gloss. Paperboards are most commonly coated with multiple coatings.

[0003] For certain applications, such as liquid packaging boards (LPB), a polyethylene (PE) layer is applied over the coated paperboard to form a laminate. The purpose of the PE layer is typically to provide a barrier and / or facilitate heat sealing when forming a package from the laminate. During use of the laminate, it is important that the PE layer adheres firmly to the coated paperboard, i.e., delamination is avoided.

[0004] Furthermore, in applications such as LPB, it is desirable that the final packaging material has good printability. Printability is determined by several different factors, one of which is the roughness of the surface to be printed, i.e., the surface of the coated paperboard. Summary of the Invention

[0005] The inventors have recognized a need to improve polyethylene (PE) adhesion and the surface roughness of coated paperboards while optimizing binder use.

[0006] Accordingly, the present disclosure provides a coated paperboard comprising a paperboard substrate and a coating, wherein:

[0007] - the coating comprises a pigment mixture and a binder in a dry weight ratio in the range of 100:14 to 100:25;

[0008] - the pigment mixture comprises a calcium carbonate pigment and a clay pigment in a dry weight ratio in the range of 98:2 to 92:8; and

[0009] - the calcium carbonate pigment has a particle size distribution (wt.% < 2 μm) in the range of 75 to 95.

[0010] The coated paperboard according to the present disclosure surprisingly improves PE adhesion and reduces surface roughness. The combination of fine calcium carbonate pigment and a small amount of plate-like clay pigment enables optimal binder use, thereby improving PE adhesion of the coated paperboard and reducing surface roughness.

[0011] The pigment mixture may comprise a calcium carbonate pigment and a clay pigment in a dry weight ratio in the range of 98:2 to 94:6.

[0012] The calcium carbonate pigment and the clay pigment may account for 100 wt.% of the pigment mixture.

[0013] The binder used in the present disclosure may be a styrene-acrylic copolymer or a styrene-butadiene copolymer. The binder is preferably a styrene-acrylic copolymer.

[0014] The binder may be a starch-based binder. Using a starch-based binder has the advantage of being bio-based and thus having a smaller impact on the environment.

[0015] The coating may further include co-binders such as polyvinyl alcohol (PVOH), carboxymethyl cellulose (CMC) and / or starch.

[0016] The calcium carbonate pigment may be ground calcium carbonate. The fact that the calcium carbonate pigment is ground calcium carbonate can further improve the use of the binder.

[0017] The coating of the present disclosure may be a top coating. If the cardboard is laminated, the top coating may be in direct contact with the PE layer.

[0018] The coating may include a pigment mixture and a binder, and the dry weight ratio thereof is in the range of 100:16 to 100:25.

[0019] The calcium carbonate pigment may have a particle size distribution (wt.% < 2 μm) in the range of 75 to 90.

[0020] The coating weight of the coating may be 5 - 16 g / m 2 , preferably 6 - 10 g / m 2 .

[0021] The coated cardboard may further include a primer layer disposed between the cardboard substrate and the coating. The primer layer preferably primes the surface.

[0022] The total coating weight of the primer layer and the coating may be 10 - 18 g / m 2 , preferably 12 - 16 g / m 2 . The inventors have surprisingly found that by using the coating according to the present disclosure, the primer layer and / or the coating can be applied at a coating weight lower than that of conventional coatings while still maintaining or improving the properties of the coated cardboard, such as surface roughness and PE adhesion. The lower coating weight can reduce the cost of the coated cardboard and its impact on the environment.

[0023] The coated paperboard may have a Parker Print Surf (PPS) roughness of 3.2 μm or lower, such as 3.2 - 0.5 μm, preferably 3 μm or lower, such as 3 - 0.5 μm. The PPS roughness is measured according to ISO 8791-4. Additionally, the coated paperboard may have a Bendtsen roughness of 250 ml / min or lower, such as 250 - 25 ml / min, preferably 200 ml / min or lower, such as 200 - 25 ml / min. The Bendtsen roughness is measured according to ISO 8791-2. The low surface roughness shown by the PPS and Bendtsen values can result in improved printability of the coated paperboard.

[0024] The paperboard can be a liquid packaging board (LPB).

[0025] Furthermore, according to a second aspect of the present invention, the paperboard substrate of the liquid packaging board comprises at least two layers, such as at least three plies. Optionally, each ply comprises a hydrophobic sizing agent. The hydrophobic sizing agent can be alkenyl succinic anhydride (ASA), alkyl ketene dimer (AKD), and / or rosin sizing agent, and each ply of the paperboard substrate can comprise at least 1.5 kg / ton of fiber of the hydrophobic sizing agent. Preferably, each ply comprises at least one of AKD and ASA.

[0026] The hydrophobic sizing agent is preferably added as internal sizing. Description of the Drawings

[0027] Aspects and embodiments will now be described by way of example with reference to the accompanying drawings, in which:

[0028] Figure 1a The Parker Print Surf roughness of the coated paperboard in Example 1 is shown.

[0029] Figure 1b The Bendtsen roughness of the coated paperboard in Example 1 is shown.

[0030] Figure 2 The PE adhesion of the coated paperboard in Example 1 is shown.

[0031] Figure 3 The topology of the coated paperboard determined by Optitopo measurement is shown.

[0032] Figure 4a The Parker Print Surf roughness of the coated paperboard in Example 2 is shown.

[0033] Figure 4b The Bendtsen roughness of the coated paperboard in Example 2 is shown.

[0034] Figure 5Shows the PE adhesion of the coated cardboard in Example 2. Detailed Description

[0035] The present disclosure relates to a cardboard coated with a coating, the coating having a pigment mixture comprising fine calcium carbonate pigment and a small amount of clay pigment.

[0036] The cardboard substrate may comprise at least two plies, such as at least three plies, wherein the top ply of the cardboard substrate is provided with a coating. The top ply of the cardboard substrate is typically bleached. Each ply of the cardboard substrate may comprise a hydrophobic sizing agent, such as ASA, AKD and / or rosin sizing agent. The addition amount of the hydrophobic sizing agent may be at least 1.5 kg / ton of fiber.

[0037] The cardboard substrate may include other conventional additives, such as fillers and colorants, but this is optional.

[0038] The coating comprises a pigment mixture and a binder, with a dry weight ratio of 100:14 to 100:25. Those skilled in the art understand that for every 100 parts of pigment, 14 - 25 parts of binder can be added to the coating. Preferably, the coating comprises a pigment mixture and a binder with a dry weight ratio of 100:16 to 100:25, and more preferably, 100:16 to 100:23.

[0039] The binder may be a synthetic binder and / or a bio - based binder. Suitable bio - based binders may include polysaccharides, such as cellulose and starch - based binders. Suitable synthetic binders may include styrene copolymers and polyvinyl alcohol.

[0040] The synthetic binder is preferably a styrene copolymer, such as a styrene - acrylic copolymer or a styrene - butadiene copolymer. Styrene - butadiene copolymer can be a lower - cost alternative, while styrene - acrylic copolymer has been shown to have advantages in applications where requirements for taste and odor are present, such as food packaging. For example, from the perspective of environment and health, styrene - acrylic copolymer is also preferred.

[0041] The bio - based binder is preferably a starch - based binder. An example of a starch - based binder is a starch granule dispersion, preferably starch nanoparticles, i.e., biolatex. The starch - based binder may include cross - linked starch nanoparticles.

[0042] The binder is typically the most expensive component in the coating and thus its use needs to be optimized to reduce the amount of binder required. The pigment mixture of the present disclosure enables the optimal use of the binder, that is, due to this specific pigment mixture, a reduction in the amount of binder can be achieved while maintaining or improving the PE adhesion and surface roughness.

[0043] Without being bound by any theory, it should be considered that the pigment mixture according to the present disclosure provides good cohesion between the binder and the pigment by efficiently utilizing the binder. This improves the resistance to damage caused by forces acting on the coating, such as during delamination of a laminated PE layer. This optimized use of the binder may be due to an improved interface between the binder and the pigment particles, which reduces the number of weak points in the coating (parts of the coating where the pigment is not bound to the cardboard surface). Thus, the coatings according to the present disclosure enable good cohesion between the binder and the pigment particles, improve the resistance of the coating to damage, and thereby also improve the adhesion of the PE to the coating.

[0044] The pigment mixture comprises a calcium carbonate pigment and a clay pigment. The dry weight ratio between calcium carbonate and clay is in the range of 98:2 to 92:8. Preferably, the dry weight ratio between calcium carbonate and clay is in the range of 98:2 to 94:6.

[0045] The calcium carbonate pigment and the clay pigment may be the only pigments in the pigment mixture and thus account for 100 wt.% of the pigment mixture, meaning that 100% of the pigments present in the coating are the calcium carbonate pigment and the clay pigment as defined herein. Additionally, the calcium carbonate pigment may be the only calcium carbonate pigment present in the pigment mixture.

[0046] The calcium carbonate pigment has a particle size distribution (wt.% < 2 μm) in the range of 75 to 95. Preferably, the calcium carbonate pigment has a particle size distribution (wt.% < 2 μm) in the range of 75 to 90. The calcium carbonate pigment has a D 50 (number average) that may be 0.7 μm ± 0.6 μm. Additionally, the calcium carbonate pigment has a D 98 (number average) that may be 3.2 μm ± 0.5 μm.

[0047] Those skilled in the art understand that "particle size distribution (wt.% < 2 μm) between 75 and 95" means that the particles between 75 wt.% and 95 wt.% have an equivalent spherical diameter of less than 2 μm.

[0048] "wt.% < 2 μm" is a commonly used cut-off value in the art for defining the particle size of pigment products. For example, in Omya's product "HydroCarb 90", "90" represents the weight percentage of particles having a diameter less than 2 μm. "Hydrocarb 90" is considered to include fine particles.

[0049] The calcium carbonate pigment may be ground calcium carbonate (GCC).

[0050] It has been confirmed that a coating including fine calcium carbonate pigment and a small amount of clay can provide excellent PE adhesion. In this case, delamination occurs within the cardboard rather than at the interface between the coating and the PE layer. This may be particularly important when used in applications such as liquid packaging boards. In addition to the improved PE adhesion, using the coating according to the present disclosure can also result in a reduced surface roughness, i.e., reduced PPS and Bentz roughness values. The low surface roughness of the coated cardboard can improve the printability of the final material.

[0051] The cardboard may include one or more additional coatings disposed between the cardboard and the coating. The additional coatings disposed between the cardboard and the coating can be one or more primer coats and / or one or more barrier layers. One or more primer coats can be added to prime the cardboard before applying the coating and to smooth the cardboard surface. One or more primer coats preferably include coarser particles and more clay than the coating. The barrier layer can be applied to the coated cardboard to cause a barrier to water and / or oxygen.

[0052] Preferably, the coated cardboard includes a primer coat disposed between the cardboard and the coating. The primer coat can include a binder and a pigment. The binder is preferably a styrene copolymer, such as a styrene-acrylic copolymer or a styrene-butadiene copolymer. The pigment is preferably calcium carbonate and / or clay.

[0053] The coating weight of the coating can be 5 - 16 g / m 2 , preferably 7 - 10 g / m 2 . In addition, the coating can be a top coat and can be arranged such that it is in direct contact with the PE layer (if present).

[0054] If a primer coat is present, the combined coating weight of the primer coat and the coating can be 10 - 18 g / m 2 , preferably 12 - 16 g / m 2 . Preferably, the coating weight of the coating is higher than the coating weight of the primer coat, such as at least 1 g / m higher 2 . The pigment mixture according to the present disclosure can apply the coating at a lower coating weight than conventional coating materials, which can result in reduced costs and a lower environmental impact.

[0055] The coating and / or any additional coating can include a co-binder, such as polyvinyl alcohol (PVOH), carboxymethyl cellulose (CMC), and / or starch.

[0056] The coating and / or any additional layer can further include a rheology modifier, such as an alkali-swellable emulsion based on acrylate, starch, and / or CMC.

[0057] Additives present in the coating such as co - binders and / or rheological modifiers can be present in a pigment - to - additive ratio in the range of 100:5 to 100:0, wherein the pigment - to - co - binder ratio can be in the range of 100:3 to 100:0.

[0058] According to the present disclosure, starch can be used as a binder, co - binder, and / or rheological modifier. Two or three different starches can be used as different components. For example, a starch - based binder can be used together with a starch - based co - binder and a starch - based rheological modifier, and these three starches are three different starches. When used as a binder, the addition amount of starch is within the binder - to - pigment ratio according to the present disclosure; while when used as a co - binder or rheological modifier, the amounts are generally in the ranges of 100:3 to 100:0 and 100:2 to 100:0 respectively.

[0059] The inventors have found that low surface roughness as shown by PPS and Bentham values improves the printability of coated paperboard. The coated paperboard of the present disclosure can have a Parker print surface roughness of 3.2 μm or lower, such as 3.2 - 0.5 μm, preferably 3 μm or lower, such as 3 - 0.5 μm, and a Bentham roughness of 250 ml / min or lower, such as 250 - 25 ml / min, preferably 200 ml / min or lower, such as 200 - 25 ml / min. PPS and Bentham surface roughness are measured according to ISO 8791 - 4 and ISO 8791 - 2 respectively.

[0060] By using a pigment mixture comprising CaCO with a specific particle size distribution 3 and a small amount of clay, the coating according to the present disclosure produces improved PE adhesion. The improved PE adhesion will reduce the risk of delamination during package forming. In addition, compared with traditional coatings, a smoother surface and lower surface roughness can be obtained at a similar or lower coating weight. The smoother surface of the coating according to the present disclosure can further result in improved printability.

[0061] Examples

[0062] Example 1

[0063] Machine trials were carried out by coating an uncoated paperboard (LPB) substrate. The paperboard had a grammage of ~175 gsm and consisted of three plies, where the top ply was bleached. All plies included a hydrophobic sizing agent (AKD + rosin sizing agent).

[0064] Two different coating structures were evaluated. The first included a single coating (Concept 1), where the cardboard substrate was coated with only one coating. The second coating structure included two coatings (Concepts 2 and 3), where the cardboard substrate was first coated with a primer coat and then with a top coat (hereinafter referred to as the top coat). The coating formulations used in the machine tests can be seen in Table 1.

[0065] The primer coat (applied in Concepts 2 and 3) was directly applied onto the cardboard substrate using a knife coater, and the coating weight was 6 g / m 2 . Similarly, the top coat (applied in all three concepts) was directly applied onto the cardboard substrate (Concept 1) or onto the primer coat (Concepts 2 and 3) using a knife coater, and the coating weight was 8 g / m 2 . The formulations and coating structures can be seen in Table 1 and Table 2 respectively. Ensure that the top coat covers the entire surface well, as poor coverage may have a negative impact on surface roughness.

[0066] Table 1. Coating formulations used in Example 1.

[0067]

[0068]

[0069] Table 2. Coating concepts used in Example 1.

[0070] <![CDATA[Concept 1 (g / m 2 )]]> <![CDATA[Concept 2 (g / m 2 )]]> <![CDATA[Concept 3 (g / m 2 )]]> Precoat - 6 6 Topcoat 1 8 8 - Topcoat 2 - - 8 <![CDATA[Total coating weight (g / m 2 )]]> 8 14 14

[0071] For example, the coating components used in the machine tests were:

[0072] - Binder 1 - Acronal S 728, a styrene - acrylic latex.

[0073] - Calcium carbonate 1 - Hydrocarb 60 (“HC 60”). HC 60 has a d 50 of 1.4 μm, and a particle size distribution (% < 2 μm) of 60;

[0074] - Calcium carbonate 2 - Hydrocarb 90 (“HC 90”). HC 90 has a d 50 of 0.7 μm, a d 98 of 3.2 μm, and a particle size distribution (wt.% < 2 μm) of 90;

[0075] - Calcium carbonate 3 - Covercarb 75 (“CC 75”). CC 75 has a d 50 of 0.63 μm, a d 98 of 2.8 μm, and a particle size distribution (wt.% < 2 μm) of 98;

[0076] - Clay - Capim BK1. Capim BK1 has a d 50 of 0.75, an aspect ratio of 22, and a particle size distribution (wt.% < 2μm) of 85.

[0077] - RM - Archroma Cartacoat RM 15, an alkali - soluble emulsion.

[0078] The calcium carbonate pigment is obtained from Omya, the clay pigment is obtained from Imerys, and the binder is obtained from BASF. Formulations of different concepts are given in "parts", which means parts by weight. The total amount of pigments is always equivalent to 100 parts, and other components are added on this basis. For example, the formulation of Concept 3 contains 100 parts of pigments (95 parts of calcium carbonate 2 and 5 parts of clay), 18 parts of binder, and 0.42 parts of rheological modifier. This formulation contains a total of 118.42 parts.

[0079] Among the evaluated concepts, Concept 3 falls within the scope of the present disclosure, while Concepts 1 and 2 are for reference.

[0080] The Parker Print Surface (PPS) roughness and the Bentz roughness of all three concepts are measured according to the standard methods ISO 8791 - 4 and ISO 8791 - 2 respectively. The results can be seen in Figure 1a and Figure 1b . The PPS and Bentz roughness follow the same trend in these three concepts and will be evaluated simultaneously and are referred to as "surface roughness".

[0081] From Figure 1a and Figure 1b it can be seen that among the three evaluated concepts, the single - coated cardboard has the highest surface roughness (PPS and Bentz). This may be due to the coating weight of Concept 1 (8 g / m 2 ) being lower than that of Concepts 2 and 3 (14 g / m 2 ).

[0082] Concept 3 shows the smoothest surface among the tested concepts, which includes a pigment mixture of 95 wt.% calcium carbonate 2 and 5 wt.% clay. The main difference between Concepts 2 and 3 lies in the pigment mixture. Concept 2 includes a mixture of two different calcium carbonates, calcium carbonate 2 (which also exists in Concept 3) and calcium carbonate 3. Compared with calcium carbonate 2, calcium carbonate 3 is a finer calcium carbonate with a narrow particle size distribution, while the pigment mixture in Concept 3 only includes calcium carbonate 2 and a small amount of clay. This clearly shows that the use of a specific pigment mixture in Concept 3 improves the surface roughness of the coated cardboard.

[0083] A polyethylene (PE) layer will be laminated on the coated side of the cardboard according to Concepts 1 - 3, and the PE adhesion will be tested according to the standard method ISO 6133.

[0084] The PE adhesion was tested on 5 cm long laminated cardboard strips with a width of 15 mm. A tensile testing machine was used to test the delamination of the PE film from the cardboard, and the results are the average of 8 samples.

[0085] The results can be seen in Figure 2 .

[0086] Concept 3 showed an average F 最大 of 3.57 N / 15 mm, while the F of Concept 2 最大 was 1.72 N / 15 mm. Thus, the F of Concept 3 最大 was approximately twice as high as the F of Concept 2 最大 . As described above, the main difference between Concepts 2 and 3 lies in the pigment mixture of the topcoat, where the pigment mixture of Concept 3 has slightly coarser calcium carbonate particles compared to the pigment mixture of the topcoat in Concept 2. The pigment mixture of Concept 3 also includes a small amount of clay. Concept 1 showed an F 最大 of 1.19 N / 15 mm and thus had the lowest F 最大 . Concept 1 includes the same coating as the topcoat in Concept 2; however, it does not include a primer coat and thus has a lower coating weight.

[0087] Surprisingly, increasing the amount of coarser calcium carbonate pigment and adding a small amount of clay significantly improved the PE adhesion of the coated cardboard.

[0088] The topography of the coated cardboard was further evaluated using OptiTopo. L&W OptiTopo is an instrument for measuring surface roughness. In addition to PPS and Bendtsen measurements, this method may also be able to estimate the printability of the coated cardboard. The results are presented in Table 3. The values obtained from the OptiTopo measurements are the OptiTopo standard deviation ("OSD"), which is a measure of the fine-scale surface deviation, and the pit values at -1.5, -3, and -5 μm, i.e., the percentage of the surface with pit depths of -1.5, -3, and -5 μm.

[0089] Table 3. Topographical results obtained from OptiTopo measurements.

[0090]

[0091] The OptiTopo measurement results show that Concept 1 has the highest OSD and pit values, and these values for Concepts 2 and 3 are significantly lower. A low pit value is desirable because the pit value estimates the risk of missing points and uncovered printed areas. Among the tested concepts, Concept 3 exhibits the lowest OSD, and in most cases, the pit values of the tested concepts are also the lowest.

[0092] The results obtained for the surface roughness, PE adhesion, and topology of the concepts evaluated in Example 1 show that Concept 3, which includes the pigment mixture of the present disclosure, exhibits lower surface roughness, improved PE adhesion, and a more suitable topology for printing compared to Reference Concepts 1 and 2.

[0093] Example 2

[0094] In Pilot Experiment 2, a cardboard (LPB) substrate was coated with a coating including the pigment mixture according to the present disclosure. The cardboard has a grammage of ~175 gsm and includes three plies, where the top ply is bleached. All plies include a hydrophobic sizing agent (AKD + rosin sizing agent).

[0095] In this example, three different coating concepts were evaluated. These coating concepts include combinations of two different pre-coatings and three different top-coatings. One pre-coating and two top-coatings include a starch-based binder, and one top-coating includes a different calcium carbonate (calcium carbonate 4) in the pigment mixture of the top-coating compared to the other two, see Table 4. Binder 2 is a starch-based bio-latex, EcoSphere 2338, from Ecosyntetix. Calcium carbonate 4 has a particle size distribution (>2 μm) of 75, and calcium carbonate 2 has a particle size distribution (wt.% <2 μm) of 90, see Example 1.

[0096] Table 4. Coating formulations of the pre-coatings and top-coatings used in Example 2.

[0097] Precoat 2 Topcoat 3 Topcoat 4 Topcoat 5 Binder 1 (parts) - - - 18 Binder 2 (parts) 14 16 18 Calcium carbonate 2 (parts) - 95 95 - Calcium carbonate 4 (parts) 80 - - 95 Clay (parts) 20 5 5 5 RM (parts) - - - 0.35 Viscosity (mPas) 1100 1100 1100 1100 Dry content (wt.%) 63 63 63 64.5

[0098] The coated cardboard of Example 2 was prepared by directly applying the pre-coating onto the cardboard substrate at a coating weight of 8.5 g / m 2 using a knife coater, and then applying the top-coating also at a coating weight of 8.5 g / m 2 using the knife coater. Further ensure that the top-coating covers the entire surface well because poor coverage may have a negative impact on the surface roughness. The coating structure can be seen in Table 5.

[0099] Table 5. Coating concepts used in Example 1.

[0100]

[0101]

[0102] In Concepts 4 and 5, the binder is a starch-based latex, which is present in the precoat in an amount of 14 parts and in the topcoat in an amount of 16 or 18 parts. Concepts 4 and 5 further include calcium carbonate having a particle size distribution (>2 μm) of 90. The pigment mixture in the topcoat 6, i.e., Coating Concept 6, includes calcium carbonate having a particle size distribution (>2 μm) of 75, which is coarser than the calcium carbonate pigment used in Concepts 3-5.

[0103] All three concepts evaluated in Example 2 fall within the scope of the present disclosure.

[0104] The Parker Print Surface (PPS) roughness and the Bentham roughness are measured according to the standard methods ISO 8791-4 and ISO 8791-2, respectively. The results can be seen in Figure 4a -b.

[0105] All three coating concepts of Example 2 exhibit similar PPS roughness, but in a slightly higher range, see Figure 4a . The slightly higher PPS may be due to the starch-based binder in Concepts 4 and 5, and the use of coarser calcium carbonate pigment in Concept 6 (the calcium carbonate pigment in Coating Concept 3 has a particle size distribution (% <2 μm) of 75, compared to 90 in Concept 3), and is considered beneficial for coatings with starch-based binders and coarser pigments. In addition, the three coatings exhibit Bentham roughness values between 46 and 73 ml / min.

[0106] A polyethylene (PE) layer is laminated on the coated side of the cardboard according to Concepts 4-6, and the PE adhesion is tested according to the standard method ISO 6133 (see the test procedure of Example 1).

[0107] Coating Concepts 4 and 5, which include a starch-based binder, exhibit F 最大 values of 2.31 and 2.53 N / 15 mm, respectively. When the binder amount is increased from 16 parts (Concept 4) to 18 parts (Concept 5), an increase in F 最大 is observed, see Figure 5 . Coating Concept 6 has a similar F 最大 , which is 2.40 N / 15 mm.

[0108] The results obtained in Examples 1 and 2 show that the coating concepts (Concepts 3-6) including the pigment mixture of the present disclosure exhibit low surface roughness and improved PE adhesion.

[0109] Although various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are intended to be illustrative and not limiting, and their scope is defined by the appended claims.

Claims

1. A coated cardboard, the coated cardboard comprising a cardboard substrate and a coating, wherein: - the coating comprises a pigment mixture and a binder in a dry weight ratio in the range of 100:14 to 100:25; - the pigment mixture comprises a calcium carbonate pigment and a clay pigment in a dry weight ratio in the range of 98:2 to 92:8; and - the calcium carbonate pigment has a particle size distribution (wt.% < 2 μm) in the range of 75 to 95.

2. The coated cardboard according to claim 1, wherein, the calcium carbonate pigment and the clay pigment account for 100 wt.% of the pigment mixture.

3. The coated cardboard according to any one of claims 1 or 2, wherein, the binder is a styrene-acrylic copolymer or a styrene-butadiene copolymer.

4. The coated cardboard according to any one of claims 1 or 2, wherein, the binder is a starch-based binder.

5. The coated cardboard according to any one of the preceding claims, wherein, the coating further comprises a co-binder such as polyvinyl alcohol, carboxymethyl cellulose and / or starch.

6. The coated cardboard according to any one of the preceding claims, wherein, the calcium carbonate pigment is ground calcium carbonate.

7. The coated cardboard according to any one of the preceding claims, wherein, The coating weight of the said coating is 5 - 16 g / m 2 .

8. The coated cardboard according to any one of the preceding claims, wherein, the coated cardboard comprises a pre-coating disposed between the cardboard substrate and the coating.

9. The coated cardboard according to claim 8, wherein, the pre-coating comprises a binder and a pigment. Optionally, the pre-coating comprises a coarser pigment than the coating.

10. The coated cardboard according to claim 8 or 9, wherein, The total coating weight of the precoat and the coating is 10 - 18 g / m 2 .

11. The coated cardboard according to any one of the preceding claims, wherein, the coated cardboard has a Parker print surface roughness of 3.2 μm or less as measured according to ISO8791-4.

12. The coated cardboard according to any one of the preceding claims, wherein, the coated cardboard has a Bentzon roughness of 250 ml / min or less as measured according to ISO8791-2.

13. The coated cardboard according to any one of the preceding claims, the coated cardboard being a liquid packaging board (LPB).

14. The coated cardboard according to claim 13, wherein, the cardboard substrate comprises at least two plies, such as three plies.

15. The coated cardboard according to claim 14, wherein, each of the plies comprises a hydrophobic sizing agent such as alkenyl succinic anhydride (ASA), alkyl ketene dimer (AKD) and / or rosin sizing agent.

16. The coated cardboard according to claim 15, wherein, each of the plies of the cardboard substrate comprises at least 1.5 kg / ton of hydrophobic sizing agent.

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